<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<title>打印金字塔</title>
	</head>

	<body>
		<script>
			var num = prompt("请输入行数");
			document.write('<p align="center">');
			for(var i = 1; i <= num; i++) {
				for(var j = 1; j <= 2 * i - 1; j++) {
					document.write("*");
				}
				document.write("</br>")
			}
		</script>
	</body>

</html>